Not Much in That Time Frame
Welcome to the RoadTrip America forums!
Well, you've already got a start. They'll be going from Kansas City (I'm assuming from your user name) to Seattle. By the most direct route, which will take them by Mount Rushmore, that is going to be a little more than 1,900 miles by the time you add in the extra miles to get to interesting places along the way. That means 4 days of serious driving, not the 27 hours the on-line mapping routines will promise. Remember that those computer programs assume you always drive the speed limit, never get slowed down by traffic, never stop for gas, or to eat, or to go to the bathroom, or sightsee, or even sleep. Really, they need to plan on at least 4 days to make the drive plus any time that they will spend actually visiting places.
And there is so much to see on or near their route, that they may want to consider adding several days for the drive. Just around Mount Rushmore, there's also Badlands National Park, Wall Drug, Wind and Jewel Caves, the Crazy Horse Memorial, and Devils Tower. At various other points, there's the Corn Palace, the Little Bighorn Battlefield, and several scenic byways in northern Idaho around Coeur d'Alene. Without going too far out of their way, they could also include visits to Yellowstone National Park and Mount Ranier.
So the first thing they and you will need to do is to sit down and decide which of those places they'd like to see, and how much additional time they can budget for the trip in order to make such visits possible. Once those decisions are made, then we can help you find some reasonably sized towns that will make decent overnight locations and will have a choice of motels or other accommodations.
AZBuck